The present disclosure relates to endodontic instruments, orthodontic instruments, other medical instruments, and to methods of making such instruments. Prior related medical instruments have been plagued with recurrent problems including, but not limited to, undesired lateral transportation in curved canals, difficulties with enlarging curvilinear canals while substantially maintaining the original center axis of the canals, and problems with binding and/or “screwing in” of prior NiTi instruments in such canals during endodontic or orthodontic procedures. For these and other medical procedures, there is a need for handheld probing, actuating, and/or surgical-type instruments with specific metallurgical and behavioral properties.